The present invention generally relates to an image printing apparatus such as a printer, a copier and a facsimile machine, and more particularly, to an image printing apparatus capable of printing the entire area of a sheet of paper.
FIG. 1 shows a structure of a laser printer which is one of the image printing apparatuses. Referring to FIG. 1, one of sheets of paper stacked in paper feeding units 1 is fed due to the function of a pair of resist rollers 2, toward an electrostatic latent image carrier 3 constituted by a drum-shaped photosensitive member. The photosensitive drum 3 is rotated clockwise. During this time, a circumferential surface of the photosensitive drum 3 is electrified by a charger unit 4. Then, an electrostatic latent image is formed on the surface of the photosensitive drum 3 by irradiating laser beam thereon by using a write unit 5 (an optical scanning unit). When the latent image passes a develop unit 6, it is changed to a visual image by toner particles supplied from the develop unit 6. Then the visual image is transferred to the paper by an image transfer charger 7. Thereafter, the paper is detached from the photosensitive drum 3 by a paper detaching charger 8. Then the visual image on the paper is fixed by a fixing unit 9. Finally, the paper having the fixed image is ejected to an ejection part 10 or a side-tray 11 In FIG. 1, the side-tray is kept in a folded state
After the image transfer, toner particles remaining on the photosensitive drum 3 are removed by a cleaning unit 12. Then the photosensitive drum 3 is discharged by a discharger unit 13 The laser printer further includes an exposure unit 14, a controller 15, a reversing part 16 for both-side printing, a drive motor 17, and a power supply unit 18.
Conventionally, when an image is printed on paper, as shown in FIG. 2, a peripheral surface area on the paper is kept blank, and an image is printed in an image printing area R (a shading area) surrounded by the peripheral area The illustrated paper is of a letter size (11 inches long, 81/2 inches wide; a blank area is 1/2 inches long and wide).
The reason why the image printing area R surrounded by the blank area is used, is described below. In a case where black pixels are printed in the entire of a front portion A or B in a paper feeding direction (longitudinal paper feeding having a direction indicated by an arrow (a), or lateral paper feeding having a direction indicated by an error (b)), it becomes difficult to detach the paper from the photosensitive drum 3 by the paper detaching charger 8, because the paper adheres to the photosensitive drum 3. This causes paper jamming The presence of the blank area A, B prevents paper jamming.
In a case where the fixing part 9 carries out image fixing by using a heat roller, if black pixels are printed on the entire of the front portion A or B, the paper adheres to the heat roller. Therefore, it is prevented from being detached from the heat roller. This causes paper jamming. The presence of the blank area prevents paper jamming.
For the above-mentioned reasons, the peripheral area of the paper is intentionally kept blank.
A paper detaching belt type laser printer is known. In this type, a non-image printing area is provided on a right or left side of the paper with respect to the direction of paper feeding. The non-image printing area facilitates to detach the paper from the photosensitive drum 3.
FIG. 3 shows essential parts of a conventional paper detaching belt type laser printer. A paper detaching belt 80 is arranged at an end of the photosensitive drum 3. When a sheet of paper 19 is transported in a direction of the arrow, a non-image printing area 19B (a hatched portion) is obtained due to the function of the paper detaching belt 80. In both the cases of the longitudinal paper feeding and lateral paper feeding, one side of the paper is used as a transportation reference. Therefore, an image is inhibited from being printed in an area on the one side of the paper, namely the non-image printing area 19B. As a result, in the case of the longitudinal paper feeding, it is impossible to print a reference marks used as a reference when forming punch holes In addition, it is necessary to prepare different types of feeding rollers 81 in order to handle different types of sheets of paper. In a case where a single feeding roller is provided for different paper sizes, paper jamming and skews may occur frequently.
As described previously, in conventional image printing apparatuses, after an image is transferred to paper, or is fixed thereon, the paper is detached from those parts Then the image printing area R is determined in accordance with paper sizes in order to prevent the occurrence of paper jamming, and the front portion A or B of the paper is intentionally kept blank.
However, in the conventional image printing apparatuses, it is impossible to print reference marks for punch holes Hence, it is inevitable that paper is folded in half, and a crease is used as a reference mark for forming punch holes Further, it is impossible to print points which represent pitches of a section paper, on an end portion of the paper. This is inconvenient in practical use